Push-pull amplifier



Oct. 19, 1948. L. J. HAWORTH 2,451,827

PUSH -PULL AMPLIFIER 7 Filed Aug. 1, 1945 INVENTOR LELAND J. HAWORTH ATTORNEY Patented Oct. 19, 1948 Belmont, ltIass assignor, by

inesne assignments, to the United States of America as represented by the Secretary of War Application August 1, 195JS1enial No..2 5ll8,158

1 Claim. 1

This invention relates to amplifiers, and more particularly to push-pull amplifiers.

, One object of this invention 'is to provide a push-pull amplifier having a negative feed-back circuit.

Another object is to provide a push-pull amplifier with degenerative current feed-back.

Another object is to provide a push-pull amplifier having improved linearity of response.

Another object is to provide an amplifier for supplying a current wave linear with a control voltage.

Further objects, advantages, and novel features of the invention will appear from the description of the invention herein.

The drawing is a circuit diagram illustrating the principles of the invention.

In the drawing, vacuum tubes 5 and 5' are arranged in a symmetrical push-pull circuit, and

therefore the components of the circuit pertaining to tube 5 will be described and the corresponding components pertaining to tube 5 will be designated by like numbers primed in parentheses where such components exist.

A cathode resistor 6 (6') is connected from ground to cathode I (I) of tube 5 (5'). The output from the circuit ma be taken from terminals 8 and 9 of secondary I of transformer l I. Plate I 2 (l2) may be connected to one-half I 3 (l3) of the primary M of transformer II, and plate voltage fed through the center tap l5 of primary [4. Signal voltage may be applied across terminals I6 and I! of primary l8 of transformer [9. Grid (20') of tube 5 (5) then receives signal voltage from terminal 2| (2l) of one-half 22 (22) of split secondary 23 of transformer l9. Resistor 24 (24') and condenser 25 (25') serve as grid resistor and blocking condenser respectively in the conventional manner. Terminal 26 (26') of half-secondary 22 (22') is connected to junction 21' (21) between resistor 6 (6) and cathode 1' (1). Thus, each tube is provided with a double feed-back circuit, consisting of the normal feed-back from its cathode resistor, and an additional degenerative feed-back from the cathode resistor of the other tube when the other tube is responding to signal voltage.

In operation, if one tube is cut 011 by signal voltage, the other tube assumes the burden of the cut-ofi tube. Thus there is the saving of current drain associated with push-pull circuits. When both tubes are conducting, a simple analysis of the circuit shows that the alternating com- (oLji ponents of plate currents .i1 and (i2 of tubes .5 and 5 respectively are: "0191 I 292 1+Cgg2R Or we can consider that 91:0 in Equation 3.

By proper design, it is possible to cause (c1y1+c2g2)R to be very much greater than 1 throughout all operating conditions, even though at particular periods of operation g1 or 92:0. Equation 3 then reduces to equation resulting in a high degree of linearity, since the output from terminals 8 and 9 depends on the current in primary M which is the current izi1. Again, if (0191 czgz) is substantially constant, a high degree of linearity results. The foregoing analysis is not intended to be exhaustive, but merely to indicate some of the reasons for the high degree of linearity obtained by means of this invention.

The type of feed-back involved herein may be termed current feed-back, and is particularly valuable where the plate current of the circuit is intended to respond linearly in current variation to the input voltage, and hence may find particularly useful applications where secondary I0 is utilized to drive the speaker coil of an audio amplifier, or for example, where the plate loads consist of a yoke-type coil about a cathode ray tube, where a current response linear with the input voltages is important.

The amount of feed-back voltage returned from across each cathode resistance to the grid of the other tube may be caused to depend on the frequency, for purposes of frequenc compensation or other reasons, by suitable alterations in the basic circuit of the figure. Different biasing means may be employed, or difierent types of tubes used than the triodes displayed in the figure. In short, it is the purpose of this application to disclose the invention, without attempting to describe fully the many circuit variations possible in its use.

To those skilled in the art, many variations of the invention will be apparent. Therefore, it is not desired to restrict the scope of the invention :to the precise embodiment herein disclosed.

What is claimed is:

In a push-pull circuit comprising at least two vacuum tubes each having a cathode, a plate, and .a grid adapted to receive an impressed signal, the combination of two cathode resistances, one in the cathode circuit of each of said tubes, an input transformer having a secondary which consists of two portions, said portions supplying substantially equal voltages, each such portion having two terminals, said combination being so adapted 4 that see 6f said terminals of one of said tions is electrically connected to the grid of one of said tubes, and the other terminal of said one portion is electrically connected to the cathode circuit of the other of said tubes between the cathode and the said cathode resistance thereof, and so that the one of said terminals of the other portion of said secondary which is in phase opposition to said one terminal of said one portion is electrically connected to the grid of the said other tube, and the other terminal of said other portion is electrically connected to the cathode circuit of the said one tube between the cathode and the said cathode resistance thereof.

LELAND J. HAWORTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,161,844 Babler June 13, 1939 2,295,920 Goodale Sept. 29,1942 

